The spine is a flexible column formed of a plurality of bones called vertebrae. The vertebrae are hollow and piled one upon the other, forming a strong hollow column for support of the cranium and trunk. The hollow core of the spine houses and protects the nerves of the spinal cord. The different vertebrae are connected to one another by means of articular processes and intervertebral, fibrocartilaginous bodies. Various spinal disorders may cause the spine to become misaligned, curved, and/or twisted or result in fractured and/or compressed vertebrae. It is often necessary to surgically correct these spinal disorders.
The spine includes seven cervical (neck) vertebrae, twelve thoracic (chest) vertebrae, five lumbar (lower back) vertebrae, and the fused vertebrae in the sacrum and coccyx that help to form the hip region. While the shapes of individual vertebrae differ among these regions, each is essentially a short hollow shaft containing the bundle of nerves known as the spinal cord. Individual nerves, such as those carrying messages to the arms or legs, enter and exit the spinal cord through gaps between vertebrae. When the vertebrae are articulated with each other, the bodies form a strong pillar for the support of the head and trunk, and the vertebral foramina constitute a canal for the protection of the medulla spinalis (spinal cord). In between every pair of vertebrae are two apertures, the intervertebral foramina, one on either side, for the transmission of the spinal nerves and vessels.
A typical vertebra consists of two essential parts: an anterior (front) segment, which is the vertebral body; and a posterior part—the vertebral (neural) arch—which encloses the vertebral foramen. The vertebral arch is formed by a pair of pedicles and a pair of laminae, and supports seven processes, four articular, two transverse, and one spinous, the latter also being known as the neural spine.
Two transverse processes and one spinous process are posterior to (behind) the vertebral body. The spinous process comes out the back, one transverse process comes out the left, and one on the right. The spinous process of a vertebra is directed backward and downward from the junction of the laminae (in humans), and serves for the attachment of muscles and ligaments. The spinous processes of the cervical and lumbar regions can be felt through the skin. Superior and inferior articular facets on each vertebra act to restrict the range of movement possible. These facets are joined by a thin portion of the neural arch called the pars interarticularis.
The correct curvature is obtained by manipulating the vertebrae into their proper position and securing that position with various devices. For example, screws and rods may be implanted into the pedicles and posterior portions of the vertebrae along with interbody spacers and cages between the vertebrae. Plates may be implanted on anterior and lateral portions of the vertebrae. Another option includes coupling facet joints. Yet another approach includes devices for attachment to the spinous processes of the vertebrae.
Current interspinous process fusion and non-fusion devices require a direct mid-line incision large enough to expose the affected interspinous space. Additionally, typical interspinous process devices and methods require sacrificing the supraspinous ligament, a strong fibrous cord, which connects together the apices of the spinous processes from the seventh cervical vertebra to the sacrum. The device and method of the present application includes an interspinous process approach for fusion and non-fusion surgeries that accomplishes the same placement goals as the mid-line approach. The device and method decreases the incisions size and the amount of tissue disturbed by the procedure.